Electrical discharge device



June 28, 1938. a. HOLST ET AL ELECTRICAL DISCHARGE DEV ICE Filed May 15, 1937 2 Sheets-Sheet 1 4 ak e s$ay m d mW 0 3M mWE CT m We TmGEM Wh June 28, 1938. e. HOLST ET AL ELECTRICAL DISCHARGE DEVICE Filed May 15, 1957 2 Sheets-Shae?- 2 w w a n mHWbW r can m ILHEW wsfim A M H r Q GM h Patented June 28, 1938 UNITED STATES amazes ELECTRICAL DI semen ncvroa Electric Company, a

Application May 15,

corporation of New York 1937, Serial No. 142,931

Germany May 18, 1936 Claims.

The present invention relates to electrical discharge devices of the type which utilize a condensible ionizing medium. It is especially concerned with improving the stability of operation of high pressure devices of this kind.

In the operation of discharge devices of the type specified, it is desirable to maintain the vapor density of the ionizing medium at some predetermined fixed value in order to obtain a re desired operating voltage. This may be accompllshed in some cases by providing within the discharge envelope a carefully measured portion of ionizing medium of such amount that it will be entirely vaporized during normal operation. However, in the routine fabrication of discharge devices such as high pressure lamps consisting of quartz, it is extremely dimcult to maintain the internal volume of the discharge envelope perfectly uniform for each unit. Furthermore, a variation in volume of the container will vary the vapor density resulting from the introduction of a given quantity of ionizing medium.

It is an object of the present invention to pro vide an improved means for regulating the vapor pressure within an electrical discharge device and for increasing the stability of operation of such a device.

It is known that the pressure within a sealed envelope containing an excess of a vaporizable medium depends primarily upon the temperature of the coldest point of the envelope wall. In accordance with the present invention the pressure within a discharge envelope is artificially fixed by providing in the envelope a quantity of con- 35 densible ionizing medium in excess of that which can be vaporized during normal operation and maintaining a portion of the envelope wall at a substantially constant temperature. In a. particular embodiment this latter function is accomplished by appending to the envelope a sealed container enclosing a vaporizable liquid normally in heat-exchanging relation with a region of the envelope wall. Excess heat is abstracted from such region by vaporization or boiling of the liquid and is dissipated by condensing the generated vapor at some part of the container relatively remote from the discharge envelope. The boiling temperature of the liquid may be adjusted and fixed by means of a non-condensible gas provided within the container at a desired pressure.

The particular features of the invention which are desired to be protected herein will be pointed out with particularity in the appended claims. The invention itself, together with further objects ill and advantages thereof, may best be understood from the following description taken in connection with the drawings, in which Fig. 1 represents a longitudinal section of a discharge device, specifically a lamp, suitably embodying the invention;

Fig. 2 is another view of an end portion of the same lamp;

Fig. 3 shows the lamp combined with a suitable standard and reflector;

' Fig. 4 shows an alternative modification of the invention;

Fig. 5 is a detailed view of one of the elements of Fig. 4; and

Figs. 6 and 7 represent still further modifications of which the invention is capable.

Referring particularly to Fig. 1, We have shown a discharge lamp comprising an elongated envelope lel preferably of quartz, containing cooperating discharge electrodes H and i2, and a quantity of a condensible ionizing medium such as mercury. The ionizing medium, which should be present in such quantity as not to be completely vaporized during the normal use of the lamp, is represented at id as a small globule collected in the lower end of the discharge envelope.

The electrodes it and it may suitably comprise tungsten wires to which has been applied a mixture of barium and strontium oxides, or some other strongly electron emissive substance. During the use of the device the electrodes may be supplied with heating current by means of lead-in conductors ll which are connected outside the tube with bayonet contacts W. A potential suificient to produce a discharge may be applied between the electrodes from any suitable source (not shown). In order to facilitate starting, the envelope may contain a quantity of a fixed gas. for example, argon at a pressure of about 5 millimeters.

After a predetermined period of operation of the device a portion of the ionizing medium it will become vaporized. Eventually a state of stability will be reached determined by the dimensions of the discharge envelope and the energy supplied to the discharge stream. In accordance with the present invention such stabilization should occur when only a portion of the ionizable medium has been vaporized. The vapor pressure then existing will depend on the temperature of the coolest portion of the envelope which in the contemplated arrangement is fixed by means of a. constant temperature device opera.- tively connected to the envelope.

Referring to Fig. 1, such a. device is illustrated as comprising an auxiliary container 2| attached to an end wall 23 of the discharge envelope, the arrangement being such that a portion of the container is in heat-exchanging relation with the envelope wall while a second portion of the container is disposed relatively remote from the envelope. In the particular modification shown the container and envelope are joined integrally in such a way that the wall 23 forms a common partition between them.

Within the container 2! and in heat-exchanging relation with the wall 23 there is provided a quantity of a readily vaporizable liquid 25 consisting, for example, of mercury or an organic substance such as benzyl benzoate or cetyl alcohol. This liquid should have a boiling point comparable with the wall temperature desired to be maintained and is adapted to be vaporized by absorption of heat from the wall 23 as soon as that temperature is approached. The vapors thus generated will travel toward the bulbous portion of the container moreremote from the discharge envelope where they will be cooled and condensed by contact with the container walls.

If the condensing surface available is suflicient to dissipate heat at an adequate rate, the pressure within the container will not increase materially and the boiling temperature of the liquid will remain at a substantially constant value. It will be apparent, therefore, that the portion of the envelope wall 23 which is in heat-exchanging relation with the liquid will also be held at a constant temperature corresponding to the boiling point of the liquid. The ultimate result will be that the vapor pressure within the discharge envelope itself is maintained at a substantially fixed value.

It will be understood that the temperature at which the liquid 25 will boil is determined in part by the nature of the liquid and in part by the pressure within the container 2|. This last factor can be varied in a desired manner by introducing into the container at non-condensible gas, such, for example, as argon or neon. The introduction of the gas may be accomplished after the discharge device is otherwise entirely complete. Under these conditions the gas pressure may be adjusted with a high degree of accuracy so as to produce exactly the desired boiling temperature of the enclosed liquid and the desired operation of the device.

For the successful operation of the device it is necessary that the liquid 25 remain in contact with the wall 23. In order to increase the variety of positions which may be assumed by the discharge lamp without abrogating this condition, it is advantageous to arrange the axis of the container 2| at a sharp angle, say 25 to 65 degrees, with respect to that of the discharge envelope. This being done, the lamp may be tilted from the vertical position shown in Fig. 1 to the horizontal position shown in Fig. 2 without causing the vaporizable liquid to flow away from the wall 23.

In order to facilitate boiling of the vaporizable liquid and thereby to make the temperatureregulating device more readily responsive to slight changes in temperature, it is possible to provide means for promoting the initiation of boiling. Such means may comprise sharp metallic fragments suspended in the liquid or sharp points projecting into it. In the present case we have shown for this purpose a small tubulation 27 projecting toward the end wall 23 so that its open end is below the surface of thfi llaporizflbli uid. The operation of such a tubulation in assisting boiling is well understood and need not be elaborated upon herein.

The portion of the container 2| most remote from the envelope may be additionally shielded from heat radiated from the discharge space by means of a metal sheath 34 applied extcriorly to the end wall of the envelope. This sheath may be of such nature as to act as a reflector .to retain heat within the envelope.

It is also desirable to prevent gaseous convection currents set up within the discharge envelope Ill from playing over the surface of the wall 23 which is to be maintained at a constant condensing temperature. The effect of such currents varies considerably with the position of the lamp and may produce uncertain and erratic operation unless suitable precautions are taken. In the present case, the possible effect of convection currents is minimized by means of a shield 29 formed transversely across the discharge envelope between the discharge space and the wall 23. This shield has an opening 3| which permits vapors within the discharge envelope to have ready access to the condensing surface. In order to prevent condensed vaporswhich accumulate on the upper surface of this shield from.

dropping down into the discharge space and extinguishing the are, there may be provided a flange 32 surrounding the opening 3!.

In the operation of a discharge lamp such as that illustrated, it is frequently desirable to surround the lamp with a light filter for the purpose of eliminating certain ultra-violet or other radiations from the light emitted. Such a filter is illustrated in Fig. 1 as comprising a cylindrical tube 36 surrounding the discharge envelope. In order that this tube may not interfere with the effective dissipation of heat from the container 2!, the container is allowed to project, at least partially, through the end of the tube as shown.

In Fig. 3 we have shown a lamp embodying the invention as applied in connection with an adjustable reflector 38 and a lamp standard 39 having a base Q0. The discharge lamp which in this case is to be used in horizontal position, is indicated in dotted outline at M. The element 42, also shown in clotted outline, corresponds to the container 2i described in connection with Fig. 1. It will be seen that with this container arranged at an angle to the main axis of the lamp as indicated, the position of the reflector 38 may be varied considerably without causing the vaporizable liquid to flow away from the end wall of the discharge envelope.

Where one employs a non-condensible gas as a means for fixing the boiling temperature of the vaporizable liquid, it is desirable to prevent the gas from being appreciably compressed by the vapor generated in the auxiliary container during operation of the device. Such compression will obviously increase the gas pressure and raise the temperature at which the liquid can boil.

In Fig. 4 we have illustrated a modification of the invention embodying an arrangement of parts which is effective to maintain substantially constant gas pressure within the container. In this figure there is shown an electrode 43, corresponding to the electrode I l of Fig. 1, and a portion of a discharge envelope is enclosing the same.

Appended to the end wall 45 of the envelope there is provided a container comprising a relatively small tubular portion 46 and an enlarged aieaaea bulbous portion dl preferably having a volume at least four times as great as that of the portion 46. A quantity of a vaporizable liquid 68 is disposed in the container portion 46 and the bulbous portion 41 contains a non-condensible gas as previously described.

Between the two portions of the container there is provided means for condensing vapors generated by the boiling of the liquid 48. As illustrated such means comprises a heat radiator 89 in heat-exchanging relation with the connection between the lower and upper parts of the container. This radiator, which is shown in deboiling point of the vaporizable liquid.

In order to facilitate the transmission of heat through the envelope wall, it is advantageous in some cases to provide a metallic connection between the constant temperature device and the interior of the envelope. Such a connection may comprise a metal partition forming a common wall between the container and the envelope, or more simply, a metallic element connecting them. The former possibility is illustrated in Fig. 4 and the latter in Fig. 6.

Referring to Fig. 4, it will be seen that a portion of the end wall 45 is closed by means of a hollow metallic body 5 3, for example, of tungsten, such body being sealed into the quartz by means of a transition glass 55 having an expansion coemcient intermediate between that of quartz and of tungtsen. The lower end of the body 5% projects into the discharge envelope and serves as a screen against convection currents within the envelope. An opening 58 is provided in the side of the bodyto permit entrance of the condensible ionizing medium. This opening is so positioned that it prevents condensate accumulated within the body from. flowing back into the discharge space.

In the alternative arrangement of Fig. 6 there is provided a metallic conductor 58 projecting through the end wall of the discharge envelope into a body of vaporizable liquid 59. At the end of the conductor which projects within the envelope there is provided a metallic'shield fill of substantially umbrella form adapted to perform the shielding function previously referred to. The effectiveness of the shielding may be still further increased by the use of an additional shield comprising an apertured partition 6i disposed transversely of the discharge envelope.

The discharge device shown in Fig. '7 corre-.

sponds generally to that shown in Fig. 1, and

parts corresponding to those illustrated in that figure are similarly numbered. There is additionally provided, however, a flange 65 projecting inwardly toward the discharge space from the end wall to which the temperature-regulating means is secured. Its function is to facilitate the accumulation of a body of condensed ionizing medium at the cooled region of the end wall 23.

While we have shown particular embodiments of our invention, it will be understood by those skilled in the art that many modifications may be made without departing from the invention, and we aim by the appended claims to cover all such modifications as fall within the true spirit and scope of the foregoing disclosure.

What We claim as new and desire to secure by Letters Patent of the United States is:

1. An electrical discharge device comprising an envelope enclosing discharge electrodes and a quantity of a condensible ionizing medium, an auxiliary container in good heat-exchanging relation with a portion of the wall of the envelope, a quantity of readily vaporizable liquid within the container; means associated with the container for condensing liquid vaporized therein, and an apertured shield interposed between the said envelope wall portion and the main discharge space of the envelope.

2. An electrical discharge device comprising an envelope enclosing discharge electrodes and a quantity of a condensible ionizing medium, an auxiliary container in heat exchanging relation with the wall of the envelope, av quantity of vaporizable liquid within the container and means in contact with the liquid in the container for promoting boiling thereof and means associated with the container for condensing liquid vaporized therein.

3. An electrical discharge device comprising an envelope enclosing discharge electrodes and a quantity of a readily condensible ionizing medium and means associated with the device for regulating the vapor pressure of the ionizing medium within the envelope, said means including a sealed container having a portion thereof, in heat-exchanging relation with a wall of the discharge device envelope and another portion relatively remote from the envelope, a quantity of a vaporizable medium in the first portion, a noncondensible gas in the second portion, and means arranged between the first and second portions for condensing liquid vaporized within the container.

4.1m electrical discharge device comprising an elongated envelope enclosing discharge electrodes, and a quantity of a readily condensible ionizing medium, an auxiliary container attached exteriorly to an end wall of the envelope, said container comprising a portion in heat-exchanging relation with the envelope, a bulbous portion relatively remote from the envelope and a connection between said portions, a quantity of a vaporizable liquid within the first portion of the container, a non-condensible gas within the second portion of the container and a heat radiator in heat-exchanging relation with the connection between the first and second portions of the container for condensing liquid vaporized within the container.

5. An electrical discharge device comprising an envelope consisting principally of insulating material, discharge electrodes and a quantity of a condensible ionizing medium enclosed within the envelope, a container attached to a wall of the envelope, a metallic connection between the interior of the envelope and the interior of the container, and a vaporizable liquid Within the container and in heat-exchanging relation with said metallic connection during the normal use of the discharge device, said container having a portion thereof relatively remote from the discharge device for condensing liquid vaporized within the container.

6. A discharge device according to claim 5 in which a metal shield is provided between the discharge space and the region of the envelope to which the container is attached, said shield being in good heat-exchanging relation with the metallic connection.

7. A discharge device according to claim 5 in which the metallic connection comprises a. hollow member extending between the container and the envelope and having an opening only to the interior of the envelope.

8. An electrical discharge device comprising an envelope enclosing discharge electrodes and a quantity of a readily condensible ionizing me- 15 dium, and means associated with the device for regulating the vapor pressure of the ionizing medium within the envelope, said means including a container having a portion thereof in heat exchanging relation with the interior of the discharge device and another portion thermally isolated from the discharge device, a quantity of a vaporizable medium in the first portion, a. noncondensible gas in the second portion, and heat dissipating means arranged between the first and second portions for condensing liquid vaporized within the container.

GILLES HOLST. WILLE'M ELENBAAS. AART VAN WYK. 

